Reciprocating sickles have long been used as a cutting means for hay, grains, and many other crops. Such sickles generally comprise a series of knife guards mounted on a cutter bar and extending forwardly therefrom. The sickle bar carries a plurality of generally triangular knife blades which reciprocate back and forth across the knife guards which define two side edges causing a cutting action with the knife blades. Generally the reciprocation is arranged so that the blades move between a position aligned with one guard and a position aligned with the next causing a cutting action as they move therebetween.
It is known to provide two separate sickles which overlap only in the middle so as to reduce the stresses of driving a single very long sickle. However these arrangements only operate in effect over one half of the width.
It is also known to operate two overlapping sickles in opposite phase (or 180 degree phase difference), without the presence of stationary guard cutting surfaces, so that the cutting action occurs between the two reciprocating sickles rather than between one sickle and its cooperating stationary guards.
While reciprocating sickles have been very successful in low to moderate cutting speeds, they have been less successful when attempting to cut at high speeds, e.g. speeds in excess of 10 mph. Thus alternative forms of cutter have generally been employed at these speeds.
The inherent problem with a reciprocating knife is the fact the sickle moves back and forth in a sinusoidal pattern. As a result, after the sickle finishes a cut, it decelerates, stops, then accelerates in the opposite direction. During this time there is no cutting being done and crop is gathered between the guard points and bent forward until the sickle makes its next cut. Therefore increased travel speeds result is a ragged or long stubble.